LEAPPCB's detailed analysis of pcb assembly

You may not know much about the printed circuit board, but let's look at the printed circuit board.

What is welding

The definition of welding is the process of connecting metal parts with various fusible alloy (soldering tin).The melting point of the solder is lower than that of the welded material, so that the part will be welded without being melted and then the combination of the molecules on its surface.

Classification of welding

Welding welding can be divided into soft and hard, soft soldering temperature below 450 ℃, brazing is higher than 450 ℃.Hard soldering is usually used in silver, gold, steel, copper and other metals, whose welding points are much stronger than soft welding, and the shear strength is 20-30 times that of soft welding.

Welding ensures the continuity of metals.On the one hand, between two metals by bolt connection or physical attached together, characterized by a strong metal overall, but this kind of connection is discontinuous, sometimes if the oxide of metal surface insulation film, they are even physical contact.Another disadvantage of mechanical connection with welding is that the contact continues to oxidize and lead to an increase in resistance.In addition, vibration and other mechanical shocks may also loosen joints.Welding eliminates these problems. The welding parts do not move relative to each other, and the contact surface does not oxidize. The continuous conductive path is maintained.Welding is the fusion between the two kinds of metal process, soldering under the molten state, will dissolve the part in contact with the metal, by welding of metal surface is often a thin layer of solder insoluble oxide film, flux is used to remove this layer of oxide film.

Welding process

Welding processes usually include:

The melting of the flux can remove the oxide film on the metal surface.

The molten solder floats to the surface of the impurity and the lighter flux.

Partially dissolving some of the metal that is connected to the solder;

To cool and complete the melt of metal and solder.

In order to locate the problem of the circuit function, the components must be taken from the printed circuit board for the necessary measurement. This repair process usually includes:

Removal of special components;

Testing of components;

Replacement of defective components;

Test circuit performance.